The term refers to Robert Fisk, a journalist who wrote some rather foolish anti-war stuff, and who in particular wrote a story in which he (1) recounted how he was beaten by some anti-American Afghan refugees, and (2) thought they were morally right for doing so. Hence many pro-war blogs -- most famously, InstaPundit -- often use the term "Fisking" figuratively to mean a thorough and forceful verbal beating of an anti-war, possibly anti-American, commentator who has richly earned this figurative beating through his words. Good Fisking tends to be (or at least aim to be) quite logical, and often quotes the other article in detail, interspersing criticisms with the original article's text.

Responding to an earlier declaration against the war by a group of German intellectuals, a group of American academics and intellectuals has written a response. It's basically a heavyweight group-Fisking.

'Fisk' is developing a meaning that is broader than definition #1 but more constrained than definition #4. It's coming to designate any point-by-point (attempt at) refutation of the other guy's argument. Haven't seen it with a small "f" yet, but surely that will come soon.

Brad deLong did a nice fisking of the NYT's analysis of the employment numbers.

Fisk- Doing any unspecific action. Fisk is the embodiment of life put into a single syllable. What means what ever you want. The word Fisk may or may not indirectly refer to acts involving narcotics such as marijuana, or the unplanned act of partying, as well as expressing extreme uncertainty or utter confusion

Fisk is the last name of a person that knows what's what. In some countries, like the USA, they are regarded as royalty and should be. When you get 2 or more together, the more the better, then the possibilities are endless. Most are available for parties and bar mitzvahs upon request.